The present invention relates to the decoding of digital transport streams such as MPEG-2 bitstreams, and in particular to a method and system for scheduled activation of system information tables in transport streams.
In digital television systems or services, such as those compliant with the ATSC Digital Television Standard and/or MPEG-2 protocols, tables containing various program and system information form part of the transport stream. One such table is a xe2x80x9cvirtual channel tablexe2x80x9d (in ATSC nomenclature), also known as a channel map. This channel map provides information regarding major and minor channel numbers, carrier frequencies, program numbers and other useful information for all of the virtual channels supported by the system. The virtual channel table syntax includes a xe2x80x9ccurrent_next_indicator,xe2x80x9d which indicates whether the channel map being provided is currently valid or will become valid xe2x80x9cnextxe2x80x9d (i.e. once the currently valid channel map is no longer valid). Other program and system information tables also include a xe2x80x9ccurrent_next_indicator.xe2x80x9d
When a channel map or other table is to be valid xe2x80x9cnext,xe2x80x9d the receiver cannot anticipate when the table will become xe2x80x9ccurrent.xe2x80x9d As a result, when the table becomes xe2x80x9ccurrent,xe2x80x9d it must be processed immediately in real time by the receiver. In order for channel map changes and other table changes to be reflected quickly at the receiver, the tables must be transmitted in the transport stream as frequently as possible, consuming valuable bandwidth in the transport stream. For channel maps in particular, this problem becomes more significant as increasing numbers of channels must be described in the channel maps. The channel maps must be transmitted along with a large amount of other program data such as program titles, descriptions, schedules, categories and ratings, as well as the packetized elementary streams containing audio and video data, all of which compete for the limited available bandwidth.
Therefore, a need has arisen for a method and system for handling system information tables that address the disadvantages and deficiencies of the prior art. In particular, a need has arisen for a method and system for scheduled activation of system information tables in transport streams.
Accordingly, a method for decoding a transport stream is disclosed. In one embodiment, the method includes receiving a system information table in the transport stream, reading an activation time from the system information table, storing the table in a memory without activating values contained in the system information table, determining when the activation time is reached, and activating the values contained in the system information table when the activation time is reached.
A transport stream reception system is also disclosed. In one embodiment, the system includes a receiver with a memory for storing data. The receiver also has a decoder that receives a system information table in a transport stream, reads an activation time from the system information table, stores the table in the memory without activating values contained in the system information table, determines when the activation time is reached, and activates the values contained in the system information table when the activation time is reached.
An advantage of the present invention is that the program and system information tables can be transmitted less frequently and still allow the receiver to execute the acquired xe2x80x9cnextxe2x80x9d tables in a timely manner, once the tables have been received for the first time and their activation times have arrived. Another advantage of the present invention is its backward compatibility with the existing protocol formats. This is because the present invention requires no syntactic modification to the existing table formats. Instead, a new descriptor, called activation_time_descriptor( ), is defined for inclusion in those tables that actually utilize the current_next_indicator_ to aid the processing in the receiver, such as channel tuning. As a result, the descriptor can be discarded by the receivers that do not recognize it.